Effect of Phosphoenolpyruvate and Oxaloacetate on Ca2+ Uptake by Isolated Mung Bean Mitochondria

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Abstract
Phosphoenolpyruvate partially inhibits the accumulation of Ca2+ in isolated mung bean (Phaseolus aureus Roxb.) mitochondria. Succinate-supported Ca2+ uptake is twice as sensitive to phosphoenolpyruvate inhibition as is NADH- or malate/pyruvate-supported Ca2+ uptake. Pyruvate, atractylate and ATP, but not ITP, reverse the phosphoenolpyruvate-induced inhibition. Oxaloacetic acid inhibits succinate-supported Ca2+ uptake completely while partially inhibiting NADH-supported Ca2+ uptake. The oxaloacetate inhibition of NADH-supported Ca2+ uptake is greater than that produced by phosphoenolpyruvate. Possibly inhibition of Ca2+ uptake is due to the conversion of phosphoenolpyruvate into oxaloacetate via phosphoenolpyruvate carboxykinase, with oxaloacetate responsible for the actual inhibition of Ca2+ uptake.